EP 0 620 362 B1 discloses a gas turbine assembly of the type initially mentioned, this publication forming an integral part of the present description. This comprises at least one compressor, a first combustion chamber arranged downstream of the compressor, a first turbine arranged downstream of the first combustion chamber, a second combustion chamber arranged downstream of the first turbine and a second turbine arranged downstream of the second combustion chamber. Thus, by means of the known gas turbine assembly, a gas turbine process can be implemented which operates with sequential combustion via two combustion chambers and with two turbines. The emission values can be extremely improved with the aid of sequential combustion.
A further gas turbine assembly became known from DE 103 12 971 A1, forming an integral part of the present description, and is based on the general idea of carrying out two-stage combustion in a gas turbine assembly, without a turbine, that is to say a high-pressure turbine, being interposed. Here, this gas turbine assembly puts into practice the recognition that, in a lean-burn combustion chamber, so much oxidizer usually remains in the combustion exhaust gases that, for a subsequent additional combustion stage, only a fuel still has to be supplied per se, in which case there is then only ever a lean fuel/oxidizer mixture. In the absence of a turbine between the two combustion stages or combustion chambers, as is also the case in EP 0 620 362 B1, however, relatively high exhaust gas temperatures occur downstream of the first combustion chamber and, when fuel is admixed, would lead to an immediate ignition, that is to say in the case of insufficient intermixing, to an unstructured combustion reaction during which adverse high emission values arise.
In order to avoid this problem, the publication DE 103 12 971 A1 mentioned proposes to cool the hot combustion exhaust gases of the first combustion chamber before the further fuel is introduced into the combustion exhaust gases, in order thereby to form the fuel/oxidizer mixture for the second combustion chamber. By the combustion exhaust gases of the first combustion chamber or of the first combustion stage being cooled, the exhaust gas temperature can be lowered to an extent such that the ignition of the fuel introduced is delayed until sufficient mixture formation can take place in order to form the desired lean fuel/oxidizer mixture between the combustion exhaust gases of the first combustion chamber and the fuel additionally supplied.
It is especially important in this case that the fuel taking effect in the second combustion stage can be introduced into the cooled exhaust of the first combustion stage directly, that is to say without a premix being formed. In this respect, for the supply of fuel in the second combustion stage, in particular, the proven technology, as gathered from EP 0 620 362 B1, will be adopted.
By means of the two-stage lean/lean combustion, without an interposed turbine, as may be gathered from DE 103 12 971 A1, it is possible at nominal operating point of the gas turbine assembly to achieve especially favorable emission values. Furthermore, considerable advantages for transient operating states are afforded. For example, in part-load operation, the second combustion chamber can be deactivated, while the first combustion chamber operates, as before, in its nominal operating state. The first combustion stage can thereby operate optimally with regard to emission values and efficiency, as a result of which, in these transient operating states, the gas turbine assembly possesses, overall, favorable values for emission and efficiency. Moreover, it is possible, particularly when the gas turbine assembly is being run up or for peak loads, to use the second combustion stage as a “booster”, in that correspondingly increased fuel quantities are supplied to the second combustion stage.
In this case, the combustion gases of the first combustion chamber can be cooled by means of heat transmission. Heat is thus extracted from the combustion gases and transmitted to another medium, so that it is possible to use elsewhere the heat which has been extracted from the gas turbine process. For example, the extracted heat may be used for generating steam for a steam turbine.
Alternatively, the cooling of the combustion gases of the first combustion chamber may also be achieved in that a suitable cooling medium is introduced into the combustion gases. In this procedure, the decrease in temperature of the combustion gases occurs because of intermixing with the cooler cooling medium. During such cooling, however, the mass flow is increased because of the cooling, and this may at the same time entail an increase in output of the gas turbine assembly. Cooling by a controlled introduction or injection of the cooling medium may also be utilized correspondingly as a “booster”, in order, particularly for a short time, to regulate the output of the gas turbine and assembly.
It is nevertheless still desirable, in a gas turbine assembly of the type initially mentioned, to improve the emission values and combustion chamber design even further. In combustion chamber design, it is important, in particular, to influence positively the relatively long axial length of the two sequentially arranged combustion chambers which consequently govern the distance between bearings. In particular, those combustion-related bottlenecks and interferences which are found in the case of continuous ring-shaped combustion chambers and which occur in gas turbine assemblies with high outputs are to be avoided. In summary, it can be said that it is also a primary gain in the design of such sequential combustion systems to have improved compactness of the entire gas turbine assembly.
Moreover, the following publications likewise form an integral part of the present description:                EP 0 321 809 A and B        EP 0 704 657 A and B        EP 0 646 705 A and B        EP 0 646 704 A and B        EP 0 718 470 A and BRelevant publications which contain one or more developments of one of the publications mentioned likewise form an integral part of the present description.        